1. Field of the Invention
The invention relates to a multi-band wireless transceiver for selecting a frequency band, for instance, in a mobile phone which makes wireless communication through a plurality of frequency bands such as W-CDMA (Wideband-Code Division Multiple Access) or GSM (Global System for Mobile communication).
The invention relates further to a method of such a multi-band wireless transceiver.
2. Description of the Related Art
There are many mobile communication systems for a mobile phone, such as W-CDMA, GSM, EDGE (an extended system of GSM) and CDMA 2000. Each of these systems is operated through a plurality of frequency bands. A conventional mobile communication terminal such as a mobile phone is designed to operate through a single frequency band among such a plurality of frequency bands.
FIG. 1 is a block diagram of a conventional wireless signal processor in a mobile communication terminal which operates through a single frequency band. In FIG. 1, wireless signals are received and transmitted in accordance with the direct conversion process.
The wireless signal processor illustrated in FIG. 1 is comprised of an antenna 1, a duplexer 3, a low-noise amplifier (LNA) 6, a filter 9, an orthogonal demodulator 13, a first local synthesizer 28 for signal reception, a second local synthesizer 29 for signal transmission, a reference oscillator 27, an orthogonal modulator 26, a driver amplifier 23, a filter 20, a power amplifier 17, and an isolator 14.
The duplexer 3 removes a signal-transmission band out of a wireless signal having been received through the antenna 1. Then, the wireless signal is amplified in the low-noise amplifier 6. The filter 9 removes bands other than a target frequency band out of the amplified wireless signal. Then, the wireless signal is demodulated into a base band signal in the orthogonal demodulator 13.
A base band signal is comprised of a signal RXI which is in-phase with a local signal, and a signal RXQ which is orthogonal with a local signal. Those signals RXI and RXQ are processed in a base band signal processing circuit (not illustrated) located downstream of the orthogonal demodulator 13. As a result, information contained in a received wireless signal is obtained.
The first local synthesizer 28 provides a local signal necessary for the orthogonal demodulation. In FIG. 1, the orthogonal demodulator 13 divides a frequency of a local signal by two. Hence, in the case of the direct conversion, a local oscillation frequency for signal reception is twice greater than a carrier frequency of a received signal.
The wireless signal processor illustrated in FIG. 1 includes a central processing unit (CPU) (not illustrated) which controls an operation of the mobile communication terminal. An oscillation frequency of the first local synthesizer 28 is determined in accordance with both divider data input into a divider in the first local synthesizer through three-line serial interfaces DATA, CLOCK and STROBE from the central processing unit, and an oscillation frequency of the reference oscillator 27.
Similarly, when signals are to be transmitted, a base band signal TXI having in-phase component in orthogonal modulation and a base band signal TXQ having orthogonal component in orthogonal modulation, both output from a circuit (not illustrated) for processing signals to be transmitted, are input into the orthogonal modulator 26.
Signals output from the orthogonal modulator 26 are amplified to some degree in the driver amplifier 23. Then, the filter 20 removes spurious components existing out of a target frequency band.
The power amplifier 17 amplifies the signals output from the filter 20. Then, the duplexer 3 suppresses noises and spurious components existing out of a target frequency band. Then, the signals are transmitted through the antenna 1.
The second local synthesizer 29 provides a local signal necessary for the orthogonal demodulation. In FIG. 1, the orthogonal modulator 26 divides a frequency of a local signal by two. Hence, in the case of the direct conversion, a local oscillation frequency for signal transmission is twice greater than a carrier frequency of a signal to be transmitted.
An oscillation frequency of the second local synthesizer 29 is determined in accordance with both divider data input into a divider in the second local synthesizer through three-line serial interfaces DATA, CLOCK and STROBE from the central processing unit, and an oscillation frequency of the reference oscillator 27.
In FIG. 1, the first and second local synthesizers 28 and 29 receive divider data through the common three-line serial interfaces. The divider data used for the first and second local synthesizers 28 and 29 is separated by identifying address bits included in the divider data.
FIG. 2 is a block diagram of an example of the first or second local synthesizer 28 or 29. The illustrated synthesizer divides signals by a number.
The illustrated synthesizer is comprised basically of a phase-locked loop (PLL) circuit in which a charge pump 33 is driven in accordance with a signal output from a phase-detector 34 which is indicative of a phase difference between a phase of a signal having a reference frequency, transmitted from a reference oscillator 27 and divided by an R-divider 35, and a signal transmitted from a voltage controlled oscillator 31 and divided by an N-divider 36, and an oscillation frequency of the voltage controlled oscillator 31 is negatively fed back.
An output frequency Fo, that is, an oscillation frequency of the voltage controlled oscillator 31 is defined in the following equation.Fo=Fr×N/R 
In the equation, Fr indicates a frequency of a signal generated in the reference oscillator 27, N indicates a number by which the N-divider 36 divides a signal, and R indicates a number by which the R-divider 35 divides a signal. However if the synthesizer employs fractional-N technology, the number N can be a rational number.
Accordingly, the oscillation frequency Fo is singly determined, if the frequency Fr and the numbers N and R are known.
The numbers N and R are transmitted to an N-register 39 and an R-register 40 through the three-line serial interfaces DATA, STROBE and CLOCK and further through a shift register 46 and an address decoder 45 from the central processing unit, when the STROBE signal rises up.
FIG. 3 is a timing chart of the DATA, STROBE and CLOCK signals.
Address data follows serial data comprised of divided data N and R. Only when an address indicated in the address data is coincident with an address of the synthesizer, the STROBE signal is transmitted to the N-register 39 and the R-register 40. Thus, the divided data N and R to be transmitted to the second local synthesizer 29 is differentiated from the divided data N and R to be transmitted to the first local synthesizer 28.
As mentioned above, the mobile communication terminal illustrated in FIG. 1 operates through a single frequency band.
There is a need for roaming in countries in which various frequency bands are used. Hence, for instance, Japanese Patent Application Publications Nos. 11-251951, 2001-186042, 2004-129066 and 2002-064397 suggest a mobile communication terminal which can be used in accordance with a plurality of systems or through a plurality of frequency bands.
Furthermore, W-CDMA which will be used for a third-generation mobile phone uses UMTS band (transmission: 1920-1980 MHz, reception: 2110-2170 MHz). However, it is expected that W-CDMA will be in short in a frequency band, if W-CDMA uses a single frequency band, specifically, UMTS band, because (a) W-CDMA will be rapidly popularized, (b) communication in which much data such as still and moving pictures is transmitted will be much increased, and (c) a flat-rate schedule is introduced, and hence, a user is allowed to transmit much data at low cost. Thus, it is suggested that a plurality of frequency bands such as PCS band and DCS band both used in conventional TDMA system is used for W-CDMA.
The detail of those frequency bands is as follows.
Band I (UMTS band)
signal transmission: 1920-1980 MHz
signal reception: 2110-2170 MHz
Band II (PCS band)
signal transmission: 1850-1910 MHz
signal reception: 1930-1990 MHz
Band III (DCS band)
signal transmission: 1710-1785 MHz
signal reception: 1805-1880 MHz
Further frequency bands other than the above-mentioned ones are presently used for W-CDMA. Thus, it is expected that there will be a need for a multi-band wireless transceiver.
FIG. 4 is a block diagram of a multi-band wireless transceiver designed to include the wireless signal processor illustrated in FIG. 1 to be able to operate through a plurality of frequency bands (three frequency bands in FIG. 4). Operation in transmission and reception of a signal in each of the frequency bands is identical with the operation of the wireless signal processor illustrated in FIG. 1, and hence, is not explained in detail.
In a multi-band wireless transceiver, the first local synthesizer 28, the second local synthesizer 29, the orthogonal demodulator 13, and the orthogonal modulator 26 may be commonly used for a plurality of frequency bands (three frequency bands in FIG. 4). The central processing unit determines divider data to be input into the first and second local synthesizers 28 and 29 through the three-line serial interfaces DATA, CLOCK and STROBE such that the divider data covers all carrier frequencies in the plurality of frequency bands, to thereby control an oscillation frequency thereof. The first and second local synthesizers 28 and 29 are designed to be able to output local oscillation frequency signals covering all carrier frequencies in the plurality of frequency bands.
A conventional wireless signal processor is necessary to include duplexers for all frequency bands. For instance, the multi-band wireless transceiver illustrated in FIG. 4 which operates through three frequency bands is necessary to include three duplexers 3, 4 and 5. One of the duplexers 3, 4 and 5 is electrically connected to the antenna 1 through an antenna switch 2. Thus, it is necessary to carry out switching control in the antenna switch 2 by providing a control signal to the antenna switch 2 from the central processing unit through a control bus 100.
In a path through which a received signal is processed, there do not exist a single low-noise amplifier and a single filter both of which can perfectly operate in all of the three frequency bands. Accordingly, the multi-band wireless transceiver illustrated in FIG. 4 is necessary to include three signal-reception paths for the three frequency bands, each comprised of low-noise amplifiers 6, 7, 8 and filters 9, 10, 11. Accordingly, the multi-band wireless transceiver illustrated in FIG. 4 is necessary to further include a switch 12 for selecting one of the three paths in accordance with a used frequency band. The switch 12 is controlled by a reception control signal thereto from the central processing unit through a control line bus 101.
In addition, since the low-noise amplifiers 6, 7 and 8 are not concurrently driven, it is necessary to turn off a power source providing power to a low-noise amplifier(s) associated with a non-used frequency band(s), in order to reduce power consumption. Thus, it is necessary to carry out on-off control to power sources providing power to the low-noise amplifiers 6, 7 and 8, in which case, the power sources are controlled by transmitting a control signal thereto from the central processing unit through control lines 102.
In a path through which signals to be transmitted, there do not exist a driver amplifier, a filter, a power amplifier, and an isolator all of which can perfectly operate through all of the three frequency bands. Thus, the multi-band wireless transceiver illustrated in FIG. 4 is necessary to include three signal-transmission paths in association with the three frequency bands, that is,
(a) first signal-transmission path: driver amplifier 23→filter 20→power amplifier 17→isolator 14;
(b) second signal-transmission path: driver amplifier 24→filter 21→power amplifier 18→isolator 15; and
(c) third signal-transmission path: driver amplifier 25→filter 22→power amplifier 19→isolator 16.
Since the driver amplifiers 23, 24 and 25 are not concurrently driven and the power amplifiers 17, 18 and 19 are not concurrently driven, it is necessary to turn off a power source providing power to a driver amplifier(s) and a power amplifier(s) associated with a non-used frequency band(s), in order to reduce power consumption. Thus, it is necessary to carry out on-off control to power sources providing power to the driver amplifiers 23, 24 and 25 and the power amplifiers 17, 18 and 19, in which case, the power sources are controlled by control signals from the central processing unit through control lines 103.
Thus, in order to accomplish a multi-band wireless transceiver, it would be necessary for the multi-band wireless transceiver to include a plurality of control lines to switch a frequency band, in which case, the control lines are additionally connected to an interface between a wireless signal processor and a central processing unit. As a result, an area in which wires extend on a printed wiring board would increase, and a central processing unit would have to additionally include control ports in order to carry out switch control to a plurality of switches, and further, on/off control to power sources providing power to amplifiers as active devices.
In the conventional multi-band wireless transceiver, a frequency band actually used is determined by a central processing unit. In doing so, the central processing unit, carries out switch control to the antenna switch 2, on/off control to power sources providing power to the low-noise amplifiers 6-8, switch control to the switch 12, and on/off control to power sources providing power to the power amplifiers 17-19 and the driver amplifiers 23-25 through the control lines extending therefrom. Thus, it is unavoidable that a number of interface lines between a wireless signal processor and the central processing unit increases, and the central processing unit has to have control ports to carry out such switch control and on/off control as mentioned above, though the central processing unit can have a limited number of control ports. This is a bar to reduction in size and cost for a multi-band wireless transceiver.